Collection : What are the differences between Map, Hashtable, HashMap, TreeMap, ConcurrentHashMap, LinkedHashMap?

• Map is an interface for a key-value map
• HashMap is a Map that uses a hash table for its implementation
• Hashtable is a synchronized version of HashMap
• TreeMap uses a tree to implement a map
• ConcurrentHashMap allows for multiple threads to access it at the same time safely
• LinkedHashMap preserves the iteration order that things were inserted in (others don’t provide a fixed iteration order)

A deeper discussion of the differences can be found in Advanced Java Programming.